The development of a self-contained, implantable, electro-chemical device capable of continuously monitoring the glucose levels of interstitial fluid continues to be the long range goal. Studies are being performed with an electro-catalytic system employing various formats of platinum as the glucose active sensor, a reference electrode (saturated calomel) and a counter electrode. A variety of potentiodynamic triangular sweeps between the reference electrode and the glucose active electrode have been studied, and various trapezoidal formats have been found useful in evaluating electric current changes as a function of the glucose concentration. In vitro studies employing a Krebs-Ringer buffer system to which is added a variety of concentrations of glucose, amino acids and urea have been evaluated. Novel concepts in the measurement of the electrical phenomenon have been discovered which allows for a highly satisfactory degree of reproducibility of measurement of glucose levels in buffer systems containing physiologic minimum and maximum concentrations of both amino acids and urea. Studies have been performed both with and without a membrane over the glucose active electrode and a number of suitable commercially available membrane materials have been identified. Dynamic in vitro studies will be instituted using a flow-through cell design that will allow for the quantity of measurements of the glucose electrode response as a function of changing concentrations of glucose, amino acids and urea.